1. Field of Invention
The present invention relates to a gas particulate solid system and more particularly relates to a gas particulate solid system in which a gas flow having a downward component is directed onto the surface of a slumped bed of particles.
2. Description of the Prior Art
The use of fluidised beds for combustion purposes such as burning of fossil fuels, incineration of combustible wastes etc. is well known. The process involves blowing air through a bed of particulate refractory material to maintain it in a fluidised state. The fuel is then introduced to the bed and burns within the bed which is thus maintained at operating temperature. Fluidised bed combustors are capable of high heat outputs and good heat transfer characteristics.
Spouted bed technology is also known and comprises passing a high velocity stream of gas vertically upwards through a mass of solid particles. The high velocity gas stream causes the particles to ascend rapidly in a hollowed central spout within the bed. Particles in a cone above the gas outlet are entrained while particles lying outside the cone descend slowly in a dense phase. The spouting action creates a fountain of particles above the slowly descending bed; and at lower flow rates in a deep bed, when the fountain does not break the surface it gives very high circulation rates of solid particles within the cone and a normal fluidised bed above the cone. In each case a cycle of solid particle movement is established. Although spouted bed technology is useful, for example, in drying, coating and granulation processes, solids blending, combustion, comminution and several chemical processes, it has disadvantages which include a relatively high pressure requirement to initiate stable spout operation. Also in multiple spout systems, the pressure drop across the nozzle must be high to avoid the fluid passing through only one outlet.